1. Field of the Invention
The present invention relates to an imaging lens and an image pickup apparatus, more particularly, to an imaging lens suitable to be used in a surveillance camera, a cell phone camera, an on-board camera, and the like employing an image pickup device such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor), and an image pickup apparatus having the imaging lens.
2. Description of the Related Art
Recently, image pickup devices such as CCD and CMOS which have been excessively downsized and of which the number of pixels has been excessively increased. In addition, an image pickup apparatus main body having the image pickup device has been also downsized, and thus it is also required to unweight and downsize an imaging lens mounted therein.
Meanwhile, in an on-board camera, a surveillance camera, and the like, there is required a small-sized and high-performance lens that has high antiweatherability in the range from outside air in a cold region to a vehicle inside in summer of a tropical region and can be used in the wide temperature range. In addition, in case of the on-board camera, it is also required that a part of lens exposed to the outside of a vehicle should be small.
In JP-A-2004-354888 (corresponding to U.S. Pat. No. 6,956,703B2) and JP-A-2004-61763, there is described an endoscope lens as a small sized imaging lens including, in order from an object side, a negative first lens, a positive second lens, an aperture diaphragm, a positive third lens, and a cemented lens. In addition, in Japanese Patent No. 3723637, there is described a lens for a still camera including, in order from, a negative first lens, a positive second lens convex toward an image side, an aperture diaphragm, a positive third lens, and a cemented lens.
However, since the lens described in JP-A-2004-354888 and JP-A-2004-61763 is an imaging lens for an endoscope, an F number thereof is large and the lens is formed as a dark optical system. Thus, the lens is inappropriate for a surveillance camera or an on-board camera to take a video. In addition, in a camera that is disposed in a vehicle to monitor the front side of the vehicle, there is required a bright lens that has a small F number to be able to be used even at nighttime. The lens described in Japanese Patent No. 3723637 has a long length of the whole optical system in an optical axis direction, and is not configured to be able to sufficiently correspond to the requirement of recent downsizing.